Highclere Castle, the ­Hampshire mansion used as the setting for the series, is said to need ­thousands spending on urgent ­repairs.

Hugh, 49, says the Earl of ­Carnarvon’s Jacobean-style property has leaks in the attics and roof.

However, he reckons the fee for filming the prime-time ­programme will help pay for repairs.

ITV has paid the 56-year-old Earl hundreds of thousands of pounds to use his property for three series, with a fourth starting in February.

Filming Downton usually involves just two floors of the house plus the 1,000-acre grounds.

Hugh, who plays the Earl of Grantham, said: “It is fair to say the ground-floor rooms and the first-floor bedrooms are being maintained beautifully but we did go up to the ­attics once and they have pretty much fallen apart.

“I am sure with the arrival of the show they can probably do them up a bit and repair leaks in the roof.

“Lady Carnarvon says she has lost count of the number of bedrooms there are, it is that sort of ­magnitude.”

Hugh added: “Sometimes we are amazed they let us film in there. They have the most astonishing artefacts and antiques.”

The Highclere estate has been home to the Carnarvon family since 1679. Over the last few years the castle has been bankrolled by TV and film productions.

The late Heath Ledger’s movie Four ­Feathers, King Ralph and Tom Cruise’s Eyes Wide Shut all featured the stately home.

However, Downton has turned Highclere into a world-famous ­location. One magazine even labelled the local area “Downtonia.”